At the end of the day, OP, you are the one who is either going to, or not going to, give yourself permission to have an affair. It is your choice and yours alone, and even if hundreds of MNetters came on here and told you how wonderful their affairs were (which is highly unlikely and I wouldn't believe them anyway), you are the one who will be making the decision to cheat/not cheat on DH and your DCs.
I've had two affairs - one physical and one emotional. I was, and still am, happily married (so in a different situation to you) and my DH does not know about either affair (which happened a few years ago.) I think it's hard to see an affair for what it really is, until you are no longer involved in it. But enjoyable is not a word I would use to describe either of my affairs. Exciting, thrilling and addictive, yes, at the time. But the lying and cheating and the compartmentalising and covering your tracks mean that you lose all sense of reality. You can't tell the truth from the lies. You risk everything, but convince yourself you will never be discovered.
You lose your sense of self-worth, and more importantly you lose your self-respect.
My marriage has also been affected, even though my affairs weren't discovered, because I have a huge secret that I am keeping from DH.
Whether you "slip into an abyss of insane guilt" really depends on the kind of person you are. If you are a person, like me, who thought that they were a 'good person' who would never cheat, then yes, the guilt is horrendous. But what is more painful is that you get to know yourself for who you really are - in my case, someone who had no boundaries, who felt entitled to some fun after years of being wife, mother, daughter etc, and who is basically selfish.
I can see from what you have said about your current situation with an unaffectionate marriage, living abroad, and the business venture, that you feel trapped in your marriage and your current life. Don't let those reasons lead you to making a terrible choice that you will live to regret.
And as for "you only have one life" - I remember a friend who had also been unfaithful saying that she would have something to remember when she sat in her rocking chair as an old lady. I wish I couldn't remember what I did. I wish it had never happened.